Pt/SrTiO3 photocatalyst for production of cycloalkanols and cycloalkanones from cycloalkanes

ABSTRACT

Methods of preparing Pt/SrTiO 3  photocatalysts comprising strontium titanate nanoparticles and platinum doped on a surface of the strontium titanate nanoparticles are described. Processes of oxidizing cycloalkanes to cycloalkanols and/or cycloalkanones by employing the Pt/SrTiO 3  photocatalysts are specified. A method for recycling the photocatalyst is also provided.

STATEMENT REGARDING PRIOR DISCLOSURE BY THE INVENTORS

Aspects of this technology are described in an article “Enhancement ofvisible light irradiation photocatalytic activity of SrTiO₃nanoparticles by Pt doping for oxidation of cyclohexane” published inJournal of Chemical Sciences, 2017, 129, 1687-1693, on Sep. 25, 2017,which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to a method of synthesizing a Pt/SrTiO₃photocatalyst comprising strontium titanate nanoparticles and platinumdoped on a surface of the photocatalyst and a process of producingcycloalkanols and/or cycloalkanones by oxidizing cycloalkanes utilizingthe Pt/SrTiO₃ photocatalyst.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of tiling, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

As major components in oil and national gas, alkanes serve as syntheticprecursors to many chemicals. For example, selective oxidation ofcyclohexane is a major process for producing KA-oil, which consists of amixture of cyclohexanol and cyclohexanone [Urus S. Adigüzel H and IncesuM 2016. Synthesis of novel N₄O₄ type bis(diazoimine)-metal complexessupported on mesoporous silica: Microwave assisted catalytic oxidationof cyclohexane, cyclooctane, cyclohexene and styrene Chem. Eng. J. 296,90; and Loncarevic D, Krstic J, Dostanic J, Manojlovic D, Cupic Z andJovanovic D M 2010. Cyclohexane oxidation and cyclohexyl hydroperoxidedecomposition by poly(4-vinylpyridine-co-divinylbenzene) supportedcobalt and chromium complexes Chem. Eng. J. 157, 181], KA-oil is animportant intermediate in the petrochemical industry for production ofvarious polymers such as nylon [Silva A R, Mourão T and Rocha J 2013.Oxidation of cyclohexane by transition-metal complexes with biomimeticligands Catal. Today 203, 81]. Therefore, selective oxidation ofcyclohexane is of great importance for scientific and industrialapplications. Currently, selective oxidation of cyclohexane is costlybecause it is an energy-consuming process that requires high temperatureand pressure. In addition, undesired by-products such as toluene,methyl-cyclohexane, heptene, 1-hexene, and 5-hexanal are often generatedduring the oxidation process, which lower production yield andcomplicate recovery/separation steps [Liu S, Liu Z and Kawi S 1998Liquid-phase oxidation of cyclohexane using Co-P-MCM-41 catalyst KoreanJ. Chem. Eng. 15, 510]. Scientific communities all around the globe arefocused on developing highly selective and efficient methods forselective oxidation of cyclohexane. A possible alternative process isphotocatalytic oxidation, which is widely applied in different fieldse.g. chemical production [Chen J, Cen J, Xu X and Li X 2016. Theapplication of heterogeneous visible light photocatalysts in organicsynthesis Catal. Sci. Technol. 6, 349]; water remediation [Lee S-Y andPark S-J 2013 TiO₂ photocatalyst for water treatment applications J.Ind. Eng. Chem. 19, 1761], and air purification [Luengas A, Barona A,Hort C, Gallastegui G, Platel V and Elias A 2015. A review of indoor airtreatment technologies Rev. Environ. Sci. Biotechnol. 14, 499]. Due totheir unique characteristics, transition metal oxides and semiconductorsare commonly used as heterogeneous photocatalysts [Litter M I 1999Heterogeneous photocatalysis: Transition metal ions in photocatalyticsystems Appl. Catal. B 23, 89]. However, there is a limited amount ofresearch devoted to developing photocatalysts for organic synthesis suchas selective oxidation of alkanes [Carneiro J T, Yang C-C, Moulijn J Aand Mul G 2011. The effect of water on the performance of TiO₂ inphotocatalytic selective alkane oxidation J. Catal. 277, 129; Zhong W,Qiao T, Dai J. Mao L, Xu Q, Zou G, Liu X, Yin D and Zhao F 2015.Visible-light-responsive sulfated vanadium-doped TS-1 with hollowstructure: enhanced photocatalytic activity in selective oxidation ofcyclohexane J. Catal. 330, 208; and Kim J, Ichikuni N, Hara T andShimazu S 2016. Study on the selectivity of propane photo-oxidationreaction on SBA-15 supported Mo oxide catalyst Catal. Today 265, 90,each incorporated herein by reference in their entirety].

SrTiO₃ is an oxide semiconductor and a potential photocatalyst [Yu K,Zhang C, Chang Y, Feng Y, Yang Z, Yang T, Lou L-L and Liu S 2017. Novelthree-dimensionally ordered macroporous SrTiO₃ photocatalysts withremarkably enhanced hydrogen production performance Appl. Catal. B 200;514; He G-L, Zhong Y-H, Chen M-J, Li X, Fang Y-P and Xu Y-H 2016.One-pot hydrothermal synthesis of SrTiO₃-reduced graphene oxidecomposites with enhanced photocatalytic activity for hydrogen productionJ. Mol. Catal. A 423, 70; Xu Y and Schoonen M A A 2000. The absoluteenergy positions of conduction and valence bands of selectedsemiconducting minerals Am. Mineral. 85, 543; Yu H, Ouyang S, Yan S, LiZ, Yu T and Zou Z 2011. Sol-gel hydrothermal synthesis ofvisible-light-driven Cr-doped SrTiO₃ for efficient hydrogen productionJ. Mater. Chem. 21, 11347; and Wang D, Ye J, Kako T and Kimura T 2006.Photophysical and photocatalytic properties of SrTiO₃ doped with Crcations on different sites J. Phys. Chem. B 110, 15824, eachincorporated herein by reference in their entirety]. It is possible toenhance the photocatalytic activity of SrTiO₃ in the visible lightregion by doping it with other metal or metal oxides. For instance,doping SrTiO₃ with Rh enhanced the catalytic properties of SrTiO₃photocatalyst for hydrogen production [Shen P, Lofaro Jr. J C, Woerner WR, White M G, Su D and Orlov A 2013. Photocatalytic activity of hydrogenevolution over Rh doped SrTiO₃ prepared by polymerizable complex methodChem. Eng. J. 223, 200, incorporated herein by reference in itsentirety], doping SrTiO₃ with Cr enhanced its photocatalytic activityfor the visible-light driven transformation of CO₂ to CH₄ [Bi Y, Ehsan MF, Huang Y, Jin J and He T 2015 Synthesis of Cr-doped SrTiO₃photocatalyst and its application in visible-light-driven transformationof CO₂ into CH₄ J. CO₂ Util. 12, 43, incorporated herein by reference inits entirety], and macroporous monolithic photocatalyst prepared bydoping SrTiO₃ with TiO₂ and nitrogen was used for photodegradation ofRhodamine B organic dye under visible light [Ruzimuradov O, Sharipov K,Yarbekov A, Saidov K, Hojamberdiev M, Prasad R M, Cherkashinin G andRiedel R 2015. A facile preparation of dual-phase nitrogen-dopedTiO₂SrTiO₃ macroporous monolithic photocatalyst for organic dyephotodegradation under visible light J. Eur. Ceram. Soc, 35, 1815,incorporated herein by reference in its entirety]. It was also reportedthat construction of a heterojunction by doping SrTiO₃ with Bi₂O₃facilitated degradation of tetracycline under visible light [Che H, ChenJr, Huang K, Hu W, Hu H, Liu X, Che G, Liu C and Shi W 2016.Construction of SrTiO₃/Bi₂O₃ heterojunction towards to improvedseparation efficiency of charge carriers and photocatalytic activityunder visible light J. Alloys Compd. 688, 882, incorporated herein byreference in its entirety], and utilization of BiVO₄/SrTiO₃ compositefor photocatalytic degradation of the antibiotic sulfamethoxazole undersunlight [Li Jr, Wang F, Meng L, Han M, Guo Y and Sun C 2017. Controlledsynthesis of BiVO₄/SrTiO₃ composite with enhanced sunlight-drivenphotofunctions for sulfamethoxazole removal J. Colloid Interface Sci.485, 116, incorporated herein by reference in its entirety]. Further,doping AgInS₂ nanoparticles with Pt enhanced the photocatalyticoxidation of cyanide in water under visible light [Azam E S 2014.Photocatalytic oxidation of cyanide under visible light by Pt dopedAgInS₂ nanoparticles J. Ind. Eng. Chem. 20, 4008, incorporated herein byreference in its entirety], while Pt doped TiO₂ nanoparticles [Xiong Z,Wang H, Xu N, Li H, Fang B, Zhao Y, Zhang J and Zheng C 2015.Photocatalytic reduction of CO₂, on Pt²⁴—Pt⁰/TiO₂ nanoparticles underUV/V is light irradiation: A combination of Pt²⁴ doping and Ptnanoparticles deposition J. Hydrogen Energy 40, 10049, incorporatedherein by reference in its entirety] and graphitic carbon nitride(g-C₃N₄) [Ong W-J, Tan L-L, Chai S-P and Yong S-T 2015. Heterojunctionengineering of graphitic carbon nitride (g-C₃N₄) via Pt loading withimproved daylight-induced photocatalytic reduction of carbon dioxide tomethane Dalton Trans. 44, 1249, incorporated herein by reference in itsentirety] were used for photocatalytic reduction of CO₂ to CH₄. However,these existing photocatalysts often suffer from various problemsincluding low efficiency, unsatisfactory stability and positive impacton charge recombination, which jeopardize their catalytic performance.

In view of the forgoing, one objective of the present invention is toprovide a process of oxidizing cycloalkanes to cycloalkanols and/orcycloalkanones in the presence of a Pt/SrTiO₃ photocatalyst and anoxidant. Another objective of the present disclosure is to provide amethod of preparing the Pt/SrTiO₃ photocatalyst.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect, the present disclosure relates to a processof oxidizing a cycloalkane to a cycloalkanol and/or a cycloalkanone. Theprocess involves contacting a feed mixture comprising the cycloalkaneand an oxidant with a Pt/SrTiO₃ photocatalyst thereby forming a reactionmixture, and concurrently irradiating the reaction mixture with lightthereby forming the cycloalkanol and/or the cycloalkanone, wherein thePt/SrTiO₃ photocatalyst includes (i) strontium titanate nanoparticles,and (ii) platinum doped on a surface of the strontium titanatenanoparticles, in which the platinum is present in an amount of 0.1-5.0wt % relative to a total weight of the Pt/SrTiO₃ photocatalyst.

In one embodiment, the Pt/SrTiO₃ photocatalyst has a crystallite size of8-30 nm.

In one embodiment, the Pt/SrTiO₃ photocatalyst has a BET surface area of5-25 m²/g.

In one embodiment, the Pt/SrTiO₃ photocatalyst has an absorption peak ina range of 360-380 nm, and a band gap energy of 2.5-3.6 eV.

In one embodiment, the Pt/SrTiO₃ photocatalyst has a photoluminescencepeak in a range of 380-480 nm upon excitation at a wavelength of 270-290nm.

In one embodiment, the light has a wavelength of 400-800 nm.

In one embodiment, the feed mixture is contacted with the Pt/SrTiO₃photocatalyst at a pressure of 0.5-2 atm.

In one embodiment, the feed mixture is contacted with the Pt/SrTiO₃photocatalyst at a temperature of 40-80° C.

In one embodiment, the cycloalkane is present in the feed mixture at aconcentration of 10-400 ppm.

In one embodiment, the oxidant is present in an amount of 5-30 vol. %)relative to a total volume of the feed mixture.

In one embodiment, the Pt/SrTiO₃ photocatalyst is present at aconcentration of 0.2-5.0 g of photocatalyst per liter of the reactionmixture.

In one embodiment, the oxidant is O₂.

In one embodiment, the feed mixture further comprises an inert gas.

In one embodiment, the feed mixture further comprises water.

In one embodiment, the process has a molar conversion of the cycloalkaneto the cycloalkanol and/or the cycloalkanone of greater than 40%.

In one embodiment, the cycloalkane is cyclohexane, the cycloalkanol iscyclohexanol, and the cycloalkanone is cyclohexanone.

In one embodiment, the platinum is present in an amount of 1.3-3.0 wt %relative to a total weight of the Pt/SrTiO₃ photocatalyst, the reactionmixture is irradiated with light for 1 to 4 hours, and the process has amolar conversion of the cycloalkane to the cycloalkanol and/or thecycloalkanone of greater than 95%.

In one embodiment, the process further comprises (i) recovering thePi/SrTiO₃ photocatalyst after the irradiating to obtain a recoveredPt/SrTiO₃ photocatalyst, and (ii) reusing the recovered Pt/SrTiO₃photocatalyst, which maintains photocatalytic activity for at least 4reaction cycles.

According to a second aspect, the present disclosure relates to a methodof producing a Pt/SrTiO₃ photocatalyst comprising strontium titanatenanoparticles and platinum doped on a surface of the strontium titanatenanoparticles. The method includes (i) mixing a strontium(II) salt withan acid to form a first mixture, (ii) adding a titanium(IV) alkoxide tothe first mixture to form a second mixture, (iii) sonicating, drying andcalcining the second mixture to form strontium titanate nanoparticles,(iv) mixing a platinum(II) compound with the strontium titanatenanoparticles to form a third mixture, and (v) reducing the thirdmixture with a reductant to form the Pt/SrTiO₃ photocatalyst.

In one embodiment, the platinum(II) compound is mixed with the strontiumtitanate nanoparticles under ultraviolet radiation.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is an overlay of the X-ray diffraction (XRD) patterns ofstrontium titanate nanoparticles (SrTiO₃), and Pt/SrTiO₃ photocatalystscontaining 0.5 wt % (0.5 wt % Pt/SrTiO₃), 1.0 wt % (1.0 wt % Pt/SrTiO₃),1.5 wt % (1.5 wt % Pt/SrTiO₃), and 2.0 wt % (2.0 wt % Pt/SrTiO₃) ofplatinum relative to a total weight of each Pt/SrTiO₃ photocatalyst.

FIG. 2 is an X-ray photoelectron spectroscopy (XPS) spectrum of thePt/SrTiO₃ photocatalyst containing 1.5 wt % of platinum relative to atotal weight of the Pt/SrTiO₃ photocatalyst.

FIG. 3A is a transmission electron microscope (TEM) image of strontiumtitanate nanoparticles (SrTiO₃).

FIG. 3B is a TEM image of the Pt/SrTiO₃ photocatalyst containing 1.5 wt% of platinum relative to a total weight of the Pt/SrTiO₃ photocatalyst.

FIG. 4 is an overlay of the UV-vis absorption spectra of strontiumtitanate nanoparticles (SrTiO₃), and Pt/SrTiO₃ photocatalysts containing0.5 wt % (0.5 wt % Pt/SrTiO₃), 1.0 wt % (1.0 wt % Pt/SrTiO₃), 1.5 wt %(1.5 wt % Pt/SrTiO₃), and 2.0 wt % (2.0 wt % Pt/SrTiO₃) of platinumrelative to a total weight of each Pt/SrTiO₃ photocatalyst.

FIG. 5 is an overlay of the band gap energy calculations for strontiumtitanate nanoparticles (SrTiO₃), and Pt/SrTiO₃ photocatalysts containing0.5 wt % (0.5 wt % Pt/SrTiO₃), 1.0 wt % (1.0 wt % Pt/SrTiO₃), 1.5 wt %(1.5 wt % Pt/SrTiO₃), and 2.0 wt % (2.0 wt % Pt/SrTiO₃) of platinumrelative to a total weight of each Pt/SrTiO₃ photocatalyst.

FIG. 6 is an overlay of the photoluminescence (PL) emission spectra ofstrontium titanate nanoparticles (SrTiO₃), and Pt/SrTiO₃ photocatalystscontaining 0.5 wt % (0.5 wt % Pt/SrTiO₃), 1.0 wt % (1.0 wt % Pt/SrTiO₃),1.5 wt % (1.5 wt % Pt/SrTiO₃), and 2.0 wt % (2.0 wt % Pt/SrTiO₃) ofplatinum relative to a total weight of each Pt/SrTiO₃ photocatalyst.

FIG. 7 is a graph showing the photocatalytic activity of strontiumtitanate nanoparticles (0 wt % Pt), and Pt/SrTiO₃ photocatalystscontaining 0.5 wt % (0.5 wt % Pt), 1.0 wt % (1.0 wt % Pt), 1.5 wt % (1.5wt % Pt), and 2.0 wt % (2.0 wt % Pt) of platinum relative to a totalweight of each Pt/SrTiO₃ photocatalyst for photocatalytic oxidation ofcyclohexane.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present disclosure will now be described more fullyhereinafter with reference to the accompanying drawings, in which some,but not all embodiments of the disclosure are shown.

The present disclosure will be better understood with reference to thefollowing terms and meanings set forth below. Unless defined otherwise,all technical and scientific terms used herein have the same meaning ascommonly understood to one of ordinary skill in the art.

As used herein, the words “a” and “an” and the like carry the meaning of“one or more.” Within the description of this disclosure, where anumerical limit or range is stated, the endpoints are included unlessstated otherwise. Also, all values and subranges within a numericallimit or range are specifically included as if explicitly written out.

As used herein, the term “compound” refers to a chemical entity, whetherin a solid, liquid or gaseous phase, and whether in a crude mixture orpurified and isolated.

Exemplary solvents useful for the present disclosure include, but arenot limited to, organic solvents, e.g. alcohols such as methanol,ethanol, trifluoroethanol, n-propanol, i-propanol, n-butanol, i-butanol,i-butanol, n-pentanol, i-pentanol, 2-methyl-2-butanol,2-trifluoromethyl-2-propanol, 2,3-dimethyl-2-butanol, 3-pentanol,3-methyl-3-pentanol, 2-methyl-3-pentanol, 2-methyl-2-pentanol,2,3-dimethyl-3-pentanol, 3-ethyl-3-pentanol, 2-methyl-2-hexanol,3-hexanol, cyclopropylmethanol, cyclopropanol, cyclobutanol,cyclopentanol, and cyclohexanol, amide solvents such asdimethylformamide (DMF), dimethylacetamide (DMA), andN-methyl-2-pyrrolidone (NMP), aromatic solvents such as benzene,o-xylene, m-xylene, p-xylene, and mixtures of xylenes, toluene,mesitylene, anisole, 1,2-dimethoxybenzene,α,α,α,-trifluoromethylbenzene, and fluorobenzene, chlorinated solventssuch as chlorobenzene, dichloromethane (DCM), 1,2-dichloroethane,1,1-dichloroethane, and chloroform, ester solvents such as ethylacetate, and propyl acetate, ethers such as diethyl ether,tetrahydrofuran (THF), 1,4-dioxane, tetrahydropyran, tert-butyl methylether, cyclopentyl methyl ether, and di-isopropyl ether, glycol etherssuch as 1,2-dimethoxyethane, diglyme, and triglyme, acetone,acetonitrile, propionitrile, butyronitrile, benzonitrile, dimethylsulfoxide (DMSO), water, e.g. tap water, distilled water, doublydistilled water, deionized water, and deionized distilled water, andmixtures thereof in suitable proportions.

As used herein, the term “substituted” refers to at least one hydrogenatom that is replaced with a non-hydrogen group, provided that normalvalencies are maintained and that the substitution results in a stablecompound. When a substituent is noted as “optionally substituted”, thesubstituents are selected from the exemplary group including, but notlimited to, halo, hydroxyl, alkoxy, oxo, alkanoyl, aryloxy, alkanoyloxy,amino, alkylamino, arylamino, arylalkylamino, disubstituted amines (e.g.in which the two amino substituents are selected from the exemplarygroup including, but not limited to, alkyl, aryl or arylalkyl),alkanylamino, aroylamino, aralkanoylamino, substituted alkanoylamino,substituted arylamino, substituted aralkanoylamino, thiol, alkylthio,arylthio, arylalkythio, alkylthiono, arylthiono, aryalkylthiono,alkylsulfonyl, arylsulfonyl; arylalkylsulfonyl, sulfonamide (e.g.—SO₂NH₂), substituted sulfonamide, nitro, cyano, carboxy, carbamyl (e.g.—CONH₂), substituted carbamyl (e.g. —CONHalkyl, —CONHaryl,—CONHarylalkyl or cases where there are two substituents on one nitrogenfrom alkyl, aryl, or alkylalkyl), alkoxycarbonyl, aryl, substitutedaryl, guanidine, heterocyclyl (e.g. indolyl, imidazoyl, fury, thienyl,thiazolyl, pyrrolidyl, pyridyl, pyrimidiyl, pyrrolidinyl, piperidinyl,morpholinyl, piperazinyl, homopiperazinyl and the like), substitutedheterocyclyl and mixtures thereof and the like.

As used herein, the term “alkyl” unless otherwise specified refers toboth branched and straight chain saturated aliphatic primary, secondary,and/or tertiary hydrocarbons of typically C₁ to C₁₂, preferably C₂ toC₈, and specifically includes, but is not limited to, methyl,trifluoromethyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl,isobutyl, t-butyl, pentyl, isopentyl, neopentyl, hexyl, isohexyl,3-methylpentyl, 2,2-dimethylbutyl, and 2,3-dimethylbutyl.

As used herein, the term “cycloalkane” refers to an optionallysubstituted alicyclic hydrocarbon of typically C₃ to C₃₀, preferablyC₄-C₂₀, more preferably C₅-C₁₆, and specifically includes, but is notlimited to, cyclopropane, cyclobutane, cyclopentane, cyclohexane,cycloheptane, cyclooctane, cyclononane, cyclodecane, cyclododecane,cyclotetradecane, cyclohexadecane, cyclooctadecane, cycloicosane,cyclodocosane, cyclotriacontane, decalin, adamantane,methylcyclopentane, methylcyclohexane, 1,1-dimethylcyclohexane,1,2-dimethylcyclohexane, and 1,3-dimethylcyclohexane.

As used herein, the term “cycloalkanol” refers to a cycloalkane havingat least one hydroxyl functional group (—OH) on an alicyclic ring.Exemplary cycloalkanols include, without limitation, cyclobutanol,cyclopentanol, cyclohexanol, cycloheptanol, cyclooctanol, cyclononanol,cyclodecanol, cycloundecanol, cyclododecanol, cyclopentadecanol,decahydro-2-naphthol, 1-methylcyclohexanol, 2-methylcyclohexanol,4-methylcyclohexanol, 1-ethylcyclopentanol, 1,2-dimethylcyclohexanol,2,2-dimethylcyclohexanol, 3,4-dimethylcyclohexanol,3,3,5-trimethylcyclohexanol, and 1-methylcyclohexane-1,2-diol.

As used herein, the term “cycloalkanone” refers to a cycloalkane havingat least one ketone functional group(>C═O) on an alicyclic ring.Exemplary cycloalkanones include, without limitation, cyclobutanone,cyclopentanone, cyclohexanone, cycloheptanone, cyclooctanone,cyclononanone, cyclodecanone, cycloundecanone, cyclododecanone,cyclopentadecanone, 1-decalone, 2-decalone, 2-methylcyclohexanone,3-methylcyclohexanone, 4-methylcyclohexanone, 2,2-dimethylcyclohexanone,3,3-dimethylcyclohexanone, 4,4-dimethycyclohexanone,2,6-dimethylcyclohexanone, 2,4-dimethylcyclohexanone,2,6,6-trimethylcycloheptanone, 3,3,5-trimethylcyclohexanone, and2,2,6,6-tetramethyl-cyclohexanone.

As used herein, the term “alkoxide” refers to an alkyl-O— group whereinalkyl is as previously described. Exemplary alkoxides include, but arenot limited to, methoxide, ethoxide, propoxide, isopropoxide, butoxide,isobutoxide, tert-butoxide, pentoxide, isopentoxide, hexyloxide, andheptyloxide.

The present disclosure is further intended to include all isotopes ofatoms occurring in the present compounds. Isotopes include those atomshaving the same atomic number but different mass numbers. By way ofgeneral example, and without limitation, isotopes of hydrogen includedeuterium and tritium, isotopes of carbon include ¹³C and ¹⁴C, isotopesof nitrogen include ¹⁵N, and isotopes of oxygen include ¹⁷O and ¹⁸O.Isotopically labeled compounds of the disclosure can generally beprepared by conventional techniques known to those skilled in the art orby processes and methods analogous to those described herein, using anappropriate isotopically labeled reagent in place of the non-labeledreagent otherwise employed.

An aspect of the present disclosure relates to a method of producing aPt/SrTiO₃ photocatalyst comprising strontium titanate nanoparticles andplatinum doped on a surface of the strontium titanate nanoparticles. Themethod comprises (i) mixing a strontium(II) salt with an acid to form afirst mixture, (ii) adding a titanium(IV) alkoxide to the first mixtureto form a second mixture, (iii) sonicating, drying and calcining thesecond mixture to form strontium titanate nanoparticles, (iv) mixing aplatinum(II) compound with the strontium titanate nanoparticles to forma third mixture, and (v) reducing the third mixture with a reductant toform the Pt/SrTiO₃ photocatalyst.

The method includes initially mixing a strontium(II) salt with an acidto form a first mixture. The first mixture may comprise strontium(II)salt at a concentration of 0.1-2 M, preferably 0.2-1 M, more preferably0.3-0.6 M. The strontium(II) salt may be strontium acetate, strontiumcarbonate, strontium chloride, strontium bromide, strontium iodide,strontium nitrate, strontium sulfate, strontium hydrogenphosphate,strontium phosphate, strontium hydroxide, and/or some otherstrontium(II) salts. In one embodiment, more than one type ofstrontium(II) salt may be used. In a preferred embodiment, thestrontium(II) salt is strontium acetate. The first mixture may comprisethe acid at a concentration of 0.1-18 M, preferably 1-15 M, preferably5-12 M. The acid may be an organic acid such as acetic acid, formicacid, propionic acid, benzoic acid, and/or butyric acid. In analternative embodiment, an inorganic acid, such as hydrochloric acid,sulfuric acid, nitric acid, bromic acid, iodic acid, and/or hydrofluoricacid, may be used in place of the organic acid. In a preferredembodiment, the acid is acetic acid.

The first mixture may be agitated for 0.5-6 hours, preferably 1-4 hours,more preferably 2-3 hours at a temperature of 4-40° C., preferably10-30° C., more preferably 15-25° C. Methods of agitating a mixtureinclude, without limitation, using an agitator, a vortexer, a rotaryshaker, a magnetic stirrer, a centralgal mixer, or an overhead stirrer.In one embodiment, the first mixture is mixed a spatula. In anotherembodiment, the first mixture is agitated by sonication in an ultrasonicbath or with an ultrasonic probe. In another embodiment, the firstmixture is left to stand without being stirred. In a preferredembodiment, the first mixture is agitated using a magnetic stirrer witha rotational speed of at least 250 rpm, preferably at least 400 rpm,more preferably at least 600 rpm.

The method also includes adding a titanium(IV) alkoxide to the firstmixture to form a second mixture. The titanium(IV) alkoxide may be addedto form a second mixture having a titanium(IV) alkoxide concentration of1-10 M, preferably 2-8 M, more preferably 4-6 M. The titanium alkoxidemay be titanium methoxide, titanium ethoxide, titanium butoxide,titanium propoxide, titanium isopropoxide, titanium pentoxide, titaniumtetraethoxide, and/or some other titanium(IV) alkoxides. In oneembodiment, more than one type of titanium(IV) alkoxide may be added toform the second mixture. In a preferred embodiment, the titanium(IV)alkoxide is titanium isopropoxide. The second mixture may be agitatedusing the aforementioned methods for 0.5-12 hours, preferably 2-8 hours,more preferably 4-6 hours at a temperature of 4-40° C., preferably10-30° C., more preferably 15-25° C. In an preferred embodiment, thesecond mixture is sonicated at a frequency of vibration of 20-150 kHz,preferably 30-100 kHz, more preferably 40-60 kHz for 0.5-3 hours,preferably 1-2 hours, using a sonication bath or a sonication probe toproduce a sonicated mixture. A solvent, e.g. acetone may be added to thesecond mixture prior to the sonication to facilitate the formation ofthe sonicated mixture. Alternatively, the second mixture may not besonicated but instead stirred, shaken, and/or rotated for an equivalentamount of time. In another embodiment, the second mixture may only bemixed to form a homogeneous mixture, and then left to sit for thepreviously mentioned amount of time.

A solid may form in the sonicated mixture, and the solid may beseparated from the liquid phase of the mixture and dried to form apowder. The solid may be isolated by subjecting the sonicated mixture tofiltration, centrifugation, evaporation, and/or heated evaporation. Thesolid may then be dried for 2-48 hours, preferably 8-36 hours,preferably 12-24 hours at a temperature of 60-300° C., preferably70-200° C., more preferably 80-120° C. In one embodiment, the solid maybe dried at these temperatures while being subjected to an absolutepressure of 0.001-10 mbar, 0.01-1 mbar, or 0.1-0.5 mbar. In anotherembodiment, the solid may be dried at one of the previously mentionedpressures but without heating.

The powder may be calcined for 0.5-12 hours, preferably 1-8 hours, morepreferably 3-6 hours, or about 5 hours, at a temperature of 300-600° C.,350-550° C., or 400-500° C. to form strontium titanate nanoparticles.The strontium titanate nanoparticles may be in the same shape ordifferent shapes, and may be the same size or different sizes. Thenanoparticles may be spherical, ellipsoidal, oblong, ovoidal, or someother rounded shape in an alternative embodiment, the nanoparticles maybe angular, rectangular, prismoidal, or some other angular shape, orthey may be nanorods, nanowires, or nanosprings. In a preferredembodiment, the strontium titanate nanoparticles are spherical. The sizeand shape of particles may be analyzed by techniques such as dynamiclight scattering (DLS), scanning electron microscopy (SEM) and/or atomicforce microscopy (AFM).

An average diameter (e.g., average particle diameter) of thenanoparticle, as used herein, refers to the average linear distancemeasured from one point on the nanoparticle through the center of thenanoparticle to a point directly across from it. In one embodiment, thestrontium titanate nanoparticles may have an average diameter in a rangeof 2-50 nm, 3-40 nm, 4-30 nm, or 5-20 nm. In one embodiment, thestrontium titanate nanoparticles may be clustered together asagglomerates having an average diameter in a range of 10-500 nm, 50-300nm, or 100-200 nm. As used herein, the term “agglomerates” refers to aclustered particulate composition comprising primary particles, theprimary particles being aggregated together in such a way so as to formclusters thereof, with at least 50 volume percent of the clusters havinga mean diameter that is at least 2 times the mean diameter of theprimary particles, and preferably at least 90 volume percent of theclusters having a mean diameter that is at least 5 times the meandiameter of the primary particles. In a preferred embodiment, thenanoparticles are well separated from one another and do not formagglomerates. The strontium titanate nanoparticles may be crystalline,polycrystalline, or amorphous. Preferably, the strontium titanatenanoparticles are crystalline. In one embodiment, the strontium titanatenanoparticles have a crystallite size of 5-40 nm, 10-30 nm, or 20-26 nm.In some embodiments, crystallite size is calculated based on X-raydiffraction (XRD) measurement using Scherrer equation [see Example 3].

The Brunauer-Emmet-Teller (BET) theory (S. Brunauer, P. H. Emmett, E.Teller, J. Am. Chem. Sac, 1938, 60, 309-319, incorporated herein byreference) aims to explain the physical adsorption of gas molecules on asolid surface and serves as the basis for an important analysistechnique for the measurement of a specific surface area of a material.Specific surface area is a property of solids which is the total surfacearea of a material per unit of mass, solid or bulk volume, or crosssectional area. In most embodiments, BET surface area is measured by gasadsorption analysis, preferably N₂ adsorption analysis. In a preferredembodiment, the strontium titanate nanoparticles have a BET surface areaof 15-30 m²/g, preferably 17-25 m²/g, more preferably 19-23 m²/g, orabout 20 m²/g. The surface may be mesoporous or microporous. The term“microporous” refers to a surface having an average pore diameter ofless than 2 nm, while the term “mesoporous” refers to a surface havingan average pore diameter of 2-50 nm. An average pore size of thestrontium titanate nanoparticles may be in a range of 1-40 nm, 1.2-25nm, 1.4-10 nm, preferably 1.6-5 nm, more preferably 1.8-2.5 nm.

As used herein, UV-vis spectroscopy or UV-vis spectrophotometry refersto absorption spectroscopy or reflectance spectroscopy in theultraviolet-visible spectral region. In one or more embodiments, thestrontium titanate nanoparticles have an ultraviolet visible absorptionwith an absorption peak in a range of 350-380 nm, preferably 360-375 nm,preferably 365-370 nm, or about 368 nm. As used herein,photoluminescence (PL) is light emission from any form of matter afterthe absorption of photons (electromagnetic radiation). In one or moreembodiments, the strontium titanate nanoparticles have aphotoluminescence peak in a range of 350-410 nm, preferably 360-400 nm,preferably 370-390 nm, or about 380 nm upon excitation at a wavelengthof 270-290 nm, preferably 272-288 nm, preferably 274-286 nm, preferably276-284 nm, preferably 278-282 nm, or about 280 nm.

As used herein, band gap energy, band gap, and/or energy gap refers toan energy range in a solid where no electron states can exist. In graphsof the electronic band structure of solids, the band gap generallyrefers to the energy difference (in electron volts) between the top ofthe valence band and the bottom of the conduction band in insulatorsand/or semiconductors. It is generally the energy required to promote avalence electron bound to an atom to become a conduction electron, whichis free to move within the crystal lattice and serve as a charge carrierto conduct electric current. Band gap energies for the Pt/SrTiO₃photocatalyst described herein may be obtained using opticalspectroscopies, e.g. UV-vis spectroscopy and/or electrochemicalmeasurements, e.g. cyclic voltammetry (CV) and differential pulsevoltammetry (DPV). In one or more embodiments, the strontium titanatenanoparticles have a band gap energy of 3.0-4.5 eV, preferably 3.2-4.0eV, preferably 3.4-3.8 eV, or about 3.6 eV.

The method further includes mixing the strontium titanate nanoparticlesformed above with a platinum(II) compound to form a third mixture. Asolvent, e.g. water may be added to the third mixture. The strontiumtitanate nanoparticles may present in the third mixture at aconcentration of 1-100 g/L, 10-80 g/L, 20-70 g/L, 30-60 g/L, or 40-50g/L. The platinum(II) compound may present in the third mixture at aconcentration of 1-2000 mg/L, 10-1500 mg/L, 20-1000 mg L, 30-500 mg/L,or 40-200 mg/L. The platinum(II) compound refers to a salt, complex,and/or a metallo-organic compound comprising platinum(II) ion and one ormore counter ions. The platinum(II) compound may or may not compriseadditional ligands and may be in any hydration state. Exemplaryplatinum(II) compounds include, but are not limited to, platinum(II)chloride, platinum(II) bromide, platinum(H) iodide, platinum(II)acetate, platinum(II) acetylacetonate, tetraammineplatinum(II) chloride,tetraammineplatinum(II) nitrate, potassium tetrachloroplatinate(II),sodium tetrachloroplatinate(II), tetraammineplatinum(II) hydroxide,diamminedinitritoplatinum(II),dimethyl(cycloocta-1,5-diene)platinum(II),cis-dichlorobis(triphenylphosphine)platinum(II),dichloro(cycloocta-1,5-diene)platinum(II), potassiumtrichloro(ethene)platinate(II),dichloro(1,2-diaminocyclohexane)platinum(II). In an alternativeembodiment, platinum compounds comprising platinum ions at otheroxidation states such as (I), (III), (IV), (V), and/or (VI) may be usedin addition to, or in lieu of platinum(II) compounds, such asplatinum(IV) oxide, platinum(IV) hydroxide, platinum(IV) sulfide,ammonium hexachloroplatinate, platinum(IV) bromide, platinum(IV)chloride, platinum(IV) fluoride, potassium hexachloroplatinate(IV),sodium hexachloroplatinate(IV), hexachloroplatinic acid(IV), xenonhexafluoroplatinate(V), platinum(V) fluoride, dioxygenylhexafluoroplatinate(V), and platinum(VI) fluoride. In a preferredembodiment, the platinum(II) compound is platinum(II) chloride.

In one or more embodiment, mixing the platinum(II) compound with thestrontium titanate nanoparticles to form the third mixture is conductedunder an ultraviolet (UV) light irradiation. As defined herein,ultraviolet light refers to electromagnetic radiation comprising one ormore wavelengths within the range 1-400 nm. In one embodiment, the thirdmixture may additionally be irradiated with light from the visibleand/or infrared spectra, for example, light having at least onewavelength in the range of 400 nm-1 mm. Alternatively, an irradiationsource may be fitted with a filter to block or attenuate light above 400nm. The irradiation source may be a flame, a lantern, a gas dischargelamp, an incandescent bulb, a laser, a fluorescent lamp, an electricarc, a light emitting diode (LED), a cathode ray tube, and/or sunlight.The irradiation source may have a total power output of 10-1000 W,50-750 W, or 100-500 W, and may be positioned 2-30 cm, 5-20 cm, or 10-15cm from the closest surface of the third mixture. The third mixture maybe irradiated with UV light for 0.5-12 hours. 1-6 hours, or 2-4 hours.Preferably the third mixture may be agitated while being irradiated inorder to maintain the dispersion of the mixture. However, in oneembodiment, the third mixture is not agitated while being irradiated.During irradiation the third mixture may be enclosed in a container andcooled in order to prevent overheating and/or solvent evaporation.Preferably the irradiation of the UV light causes the deposition ofplatinum onto the surface and/or within a portion of an outer layer ofthe strontium titanate nanoparticles by incorporating platinum ionswithin strontium titanate lattice, forming platinum-doped strontiumtitanate nanoparticles. In some embodiments, the platinum ions may beembedded into the pores of the strontium titanate lattice and thus notintegral to the strontium titanate lattice. In another embodiment, theplatinum ions are not incorporated into the lattice structure ofstrontium titanate and may be adsorbed on a surface (e.g. by van derWaals and/or electrostatic forces) of the strontium titanatenanoparticles. In an alternative embodiment, other metals, such aspalladium, silver, gold, or a mixture thereof may be used in additionto, or in lieu with platinum for the deposition.

In one embodiment, the platinum-doped strontium titanate nanoparticlesare collected from the irradiated third mixture and dried to form apowder. The nanoparticles may be isolated by subjecting the irradiatedthird mixture to filtration, centrifugation, evaporation, and/or heatedevaporation. The nanoparticles may then be dried for 2-48 hours,preferably 8-40 hours, preferably 14-30 hours at a temperature of30-200° C., preferably 40-150° C., more preferably 50-100° C., or about60° C. In one embodiment, the nanoparticles may be dried at thesetemperatures while being subjected to an absolute pressure of 0.001-10mbar, 0.01-1 mbar or 0.1-0.5 mbar. In another embodiment, thenanoparticles may be dried at one of the previously mentioned pressuresbut without heating.

In one or more embodiment, the platinum-doped strontium titanatenanoparticles are reduced by a reductant to form the Pt/StTiO₃photocatalyst. In a preferred embodiment, the platinum-doped strontiumtitanate nanoparticles are treated by hydrogen (H₂) at a flow rate of5-100 mL/min, 10-50 mL/min, or 15-30 mL/min at a temperature of 10-80°C., 25-70° C. or 35-60° C. for 0.5-6 hours, 1-4 hours, or 2-3 hours toform the Pt/StTiO₃ photocatalyst. The reduction may be carried out withthe presence of a solvent, e.g. methanol, ethanol, isopropanol, toluene.In another embodiment, the reduction is carried out without a solvent.Other exemplary reductant suitable for the present disclosure include,but are not limited to, formaldehyde, hydrazine, tin(II) chloride,sulfate-reducing bacteria, and hydrogenase-displaying yeast.

In one or more embodiments, the formed Pt/StTiO₃ photocatalyst comprises0.1-10 wt %, 0.5-5.0 wt %, 1.0-2.5 wt %, or 1.5-2.0 wt % of platinumrelative to a total weight of the Pt/SrTiO₃ photocatalyst. In apreferred embodiment, the platinum is in the form of metallic platinum.The presence and dispersity of metallic platinum may be observed byX-ray photoelectron spectroscopy (XPS), transmission electron microscopy(TEM) and high-resolution electron microscopy (HREM). For instance, twopeaks of Pt 4f having binding energies of 70.3 eV and 74.0 eV observedin the XPS spectra of Pt/SrTiO₃ photocatalyst containing 1.5 wt % ofplatinum relative to a total weight of the Pt/SrTiO₃ photocatalyst [seeFIG. 2] are resulted from the presence of metallic platinum in thephotocatalyst [Sen F and Gökagaç G 2007. Different sized platinumnanoparticles supported on carbon: an XPS study on these methanoloxidation catalyst J. Phys. Chem. C 111, 5715, incorporated herein byreference in its entirety]. In one embodiment, the formed Pt/StTiO₃photocatalyst comprises 30-60 wt %, 35-55 wt %, 40-50 wt %, or 42-48 wt% of strotium relative to a total weight of the Pt/SrTiO₃ photocatalyst.In one embodiment, the formed Pt/StTiO₃ photocatalyst comprises 10-35 wt%, 15-32 wt %, 20-30 wt %, or 24-28 wt % of titanium relative to a totalweight of the Pt/SrTiO₃ photocatalyst. The composition of the Pt/SrTiO₃photocatalyst including weight percentages of platinum, strontium andtitanium may be determined by elemental analysis techniques such asenergy-dispersive X-ray spectroscopy (EDX), X-ray photoelectronspectroscopy (XPS), inductively coupled plasma mass spectrometry(ICP-MS), and neutron activation analysis.

The Pt/SrTiO₃ photocatalyst may be in the form of nanoparticles, whichmay be in the same shape or different shapes, and may be the same sizeor different sizes. The nanoparticles may be spherical, ellipsoidal,oblong, ovoidal, or some other rounded shape. In an alternativeembodiment, the nanoparticles may be angular, rectangular, prismoidal,or some other angular shape, or they may be nanorods, nanowires, ornanosprings. In one embodiment, the nanoparticles may have an averagediameter in a range of 2-50 nm, 3-40 nm, 4-30 nm, or 5-20 nm. In oneembodiment, the Pt/SrTiO₃ photocatalyst may comprise nanoparticlesclustered together as agglomerates having an average diameter in a rangeof 10-500 nm, 50-300 nm, or 100-200 nm a preferred embodiment, thenanoparticles are well separated from one another and do not formagglomerates. The Pt/SrTiO₃ photocatalyst may be crystalline,polycrystalline, or amorphous. Preferably, the Pt/SrTiO₃ photocatalystis crystalline. In one or more embodiments, the Pt/SrTiO₃ photocatalysthas a crystallite size of 5-30 nm, 8-20 nm, or 12-18 nm. In certainembodiments, the crystallite size of the Pt/SrTiO₃ photocatalystdecreases as the wt % of platinum increases. Such a trend may indicatethat platinum doping on the strontium titanate nanoparticle surfacecould degrade crystallinity of the photocatalyst as a result of localdistortion of the crystal structure [Hassan M M, Khan W, Azam A andNaqvi A H 2014. Effect of size reduction on structural and opticalproperties of ZnO matrix due to successive doping of Fe ions J. Lumin.145, 160; and Pal M, Pal U, Gracia J M, Jiménez Y and Pérez-Rodriguez F2012. Effects of crystallization and dopant concentration on theemission behavior of TiO₂:Eu nanophosphors Nanoscale Res. Lett. doi:10,1186/1556-276X-7-1, each incorporated herein by reference in theirentirety].

In one or more embodiments, the Pt/SrTiO₃ photocatalyst has a BETsurface area of 5-30 m²/g, preferably 8-20 m²/g, more preferably 10-18m²/g, most preferably 10-14 m²/g. The surface may be mesoporous ormicroporous. In certain embodiments, the BET surface area of thePt/SrTiO₃ photocatalyst decreases as the wt % of platinum increases,which may be attributed to blocking of pores on strontium titanatenanoparticles by the platinum upon doping. It has been surprisinglyfound that the catalyst activity, in terms of cycloalkane oxidation,increases as the BET surface area of the Pt/SrTiO₃ photocatalystdecreases.

In one or more embodiments, the Pt/SrTiO₃ photocatalyst has anultraviolet visible absorption with an absorption peak in a range of360-380 nm, preferably 365-375 nm, preferably 370-373 nm. In one or moreembodiments, the Pt/SrTiO₃ photocatalyst has a photoluminescence peak ina range of 380-480 nm, preferably 400-460 nm, preferably 410-440 nm,preferably 420-430 nm upon excitation at a wavelength of 270-290 nm,preferably 272-288 nm, preferably 274-286 nm, preferably 276-284 nm,preferably 278-282 nm, or about 280 nm. In one or more embodiments, thePt/SrTiO₃ photocatalyst has a band gap energy of 2.5-3.6 eV, preferably2.6-3.4 eV, preferably 2.7-3.2 eV, preferably 2.8-3.0 eV.

Another aspect of the present disclosure relates to a process ofoxidizing a cycloalkane to a cycloalkanol and/or a cycloalkanone. Theprocess involves contacting a feed mixture comprising the cycloalkaneand an oxidant with a Pt/SrTiO₃ photocatalyst thereby forming a reactionmixture, and concurrently irradiating the reaction mixture with lightthereby forming the cycloalkanol and/or the cycloalkanone, wherein thePt/SrTiO₃ photocatalyst comprises strontium titanate nanoparticles andplatinum doped on a surface of the strontium titanate nanoparticles, inwhich the platinum is present in an amount of 0.1-5.0 wt % relative to atotal weight of the Pt/SrTiO₃ photocatalyst.

The Pt/SrTiO₃ photocatalyst used in the process may have properties suchas composition, crystallite size, surface area, absorption and emissionprofiles, and band gap energy, as previously described. Preferably, thePt/SrTiO₃ photocatalyst used here may have a crystallite size of 5-30nm, 8-20 nm, or 12-18 nm, a BET surface area of 5-25 m²/g, preferably10-20 m²/g, more preferably 14-18 m²/g, an ultraviolet visibleabsorption with an absorption peak in a range of 360-380 nm, preferably365-375 nm, preferably 370-373 nm, a band gap energy of 2.5-3.6 eV,preferably 2.6-3.4 eV, preferably 2.7-3.2 eV, preferably 2.8-3.0 eV, anda photoluminescence peak in a range of 380-480 nm, preferably 400-460nm, preferably 410-440 nm, preferably 420-430 nm upon excitation at awavelength of 270-290 nm, preferably 272-288 nm, preferably 274-286 nm,preferably 276-284 nm, preferably 278-282 nm, or about 280 nm. In one ormore embodiments, the Pt/SrTiO₃ photocatalyst is produced as describedpreviously and may comprise 0.1-10 wt %, preferably 0.5-5.0 wt %,preferably 1.0-2.5 wt %, preferably 1.5-2.0 wt % of platinum relative toa total weight of the Pt/SrTiO₃ photocatalyst. In one embodiment, thestrontium titanate nanoparticles may be pre-formed, or synthesized by amethod different than the method described in the previous aspect suchas hydrothermal method and sol-gel technique. In another embodiment, thestrontium titanate nanoparticles are not preformed, and are synthesizedfrom a titanium alkoxide by sonication as described previously.Strontium titanate nanoparticles may be doped with platinum by theaforementioned photo-assisted deposition method or by a different methodsuch as atomic layer deposition, sputtering, deposition-precipitation,and ion-exchange technique. In another embodiment, strontium titanatenanoparticles may be doped with a different metal, such as palladium,silver, gold, or a mixture thereof.

In one or more embodiments, the cycloalkane is present in the feedmixture at a concentration of 10-400 ppm, preferably 25-350 ppm,preferably 50-300 ppm, preferably 100-250 ppm, or about 200 ppm. In oneor more embodiments, the oxidant is present in an amount of 5-30 vol. %,preferably 6-25 vol. %, preferably 7-20 vol. %, preferably 8-15 vol. %,or about 10 vol. % relative to a total volume of the feed mixture. In apreferred embodiment, the oxidant is O₂. Other oxidants useful for thepresent disclosure include, but are not limited to, air, inorganicperoxides such as hydrogen peroxide, sodium peroxide, and bariumperoxide, and organic peroxides such as tell-butyl hydroperoxide, cumenehydroperoxide, dicumyl peroxide, tert-butyl peroxide, and tert-butylperoxybenzoate.

In one or more embodiments, the feed mixture further comprises an inertgas such as N₂, Ar, He. In a preferred embodiment, a N₂ stream at a feedrate of 10-50 L/h, 20-40 L/h, or about 30 L/h is mixed with the oxidant(e.g. O₂) before the oxidizing process. In another embodiment, the inertgas may be bubbled in the feed mixture in a sealed container for atleast 0.5 hour, 1 hour, or at least 2 hours before the oxidizingprocess.

In one or more embodiments, the feed mixture further comprises water.The water may be tap water, distilled water, bidistilled water,deionized water, deionized distilled water, reverse osmosis water,and/or some other water. In one embodiment the water is bidistilled toeliminate trace metals. Preferably the water is bidistilled, deionized,deinonized distilled, or reverse osmosis water and at 25° C. has aconductivity at less than 10 μS·cm⁻¹, preferably less than 1 μS·cm⁻¹, aresistivity greater than 0.1 MΩ·cm, preferably greater than 1 MΩ·cm,more preferably greater than 10 MΩ·cm, a total solid concentration lessthan 5 mg/kg, preferably less than 1 mg/kg, and a total organic carbonconcentration less than 1000 μg/L, preferably less than 200 μg/L, morepreferably less than 50 μg/L. Preferably the water is bidistilled,deionized, deinonized distilled, or reverse osmosis water. In oneembodiment, the water is present in the feed mixture at a concentrationof 50-700 ppm, preferably 100-600 ppm, preferably 200-500 ppm,preferably 300-400 ppm, or about 320 ppm.

In one or more embodiments, the feed mixture is contacted with thePt/SrTiO₃ photocatalyst to form a reaction mixture. In a preferredembodiment, the Pt/SrTiO₃ photocatalyst is present at a concentration of0.2-5.0 g per liter of the reaction mixture during the contacting,preferably 0.5-4.0 g/L, preferably 0.8-3.0 g/L, preferably 1.0-2.0 gL⁻¹, or about 1.2 g per liter of the reaction mixture during thecontacting.

In a preferred embodiment, the feed mixture is contacted with thePt/SrTiO₃ photocatalyst at a pressure of 0.3-4 atm, preferably 0.5-2atm, preferably 0.75-1.5 atm, or about 1 atm. In a preferred embodiment,the feed mixture is contacted with the Pt/SrTiO₃ photocatalyst at atemperature of 30-90° C., preferably 40-80° C., preferably 50-70° C., orabout 60° C.

The aforementioned reaction mixture may be concurrently irradiated withlight for 0.5-6 hours, preferably 0.75-4 hours, preferably 1-3 hours, orabout 1.5 hours. The light may be visible light having a wavelength of400-800 nm. The light may comprises one or more wavelengths within therange of 400-800 nm. Preferably an irradiation source is used whichemits a broad wavelength range of light and which comprises a portion orthe entire visible light spectrum. An irradiation source mayadditionally emit light of wavelengths below 400 nm and/or above 800 nm.In one embodiment, a filter may be used to prevent UV light fromentering the reaction mixture, for example, a filter that blocks lightwith wavelengths less than 420 nm may be used with a xenon or mercurygas discharge lamp. In another embodiment, a solution of 2 M NaNO₃ maybe placed between the reaction mixture and the irradiation source toattenuate or block light with wavelengths below 400 nm while lettingvisible light pass through. Alternatively, an irradiation source may beused which only emits light within the visible spectrum. The irradiationsource may emit a total power of 50-1000 W, preferably 100-750 W, morepreferably 250-500 W, or about 300 W, and may be positioned 2-30 cm,preferably 5-20 cm, more preferably 8-15 cm from the closest surface ofthe reaction mixture.

The oxidizing process may be carried out in vessels, tanks, containers,or small scale applications in both batch mode and continuous process(e.g. fixed-bed and fluidized-bed modes) reactors. As used herein,“continuous” refers to a process used to produce materials withoutinterruption or where the reactants are flowed and/or in motion duringthe reaction. In a preferred embodiment, a reactor with a transparentwindow is used. For example, the window may comprise glass or quartz,though in one embodiment, a polymeric material transparent to visiblelight and chemically stable with the reaction mixture may be used. Asdefined herein, “transparent” refers to an optical quality of a compoundwherein a certain wavelength or range of wavelengths of light maytraverse through a portion of the compound with a small loss of lightintensity. Here, the “transparent window” may causes a loss of less than10%, preferably less than 5%, more preferably less than 2% of theintensity of a certain wavelength or range of wavelengths of light. Inone embodiment, the reactor wall and window may comprise the samematerial, for example, a reactor may comprise quartz walls, which mayalso function as transparent windows. In some embodiments, the Pt/SrTiO₃photocatalyst is dispersed within the reaction mixture. In anotherembodiment, the Pt/SrTiO₃ photocatalyst may be present as a coatinghaving an average thickness of 0.001-1 mm, 0.01-0.5 mm, 0.05-0.4 mm, or0.1-0.3 mm on an interior surface of a reactor. In a preferredembodiment, the Pt/SrTiO₃ photocatalyst is mixed with a glass or quartzsupport at a weight ratio of about 1:50 to about 1:1, preferably about1:25 to about 1:4, preferably about 1:15 to about 1:10, and then used asa photocatalyst in the reaction mixture. The reaction mixture may beagitated using methods described previously while being irradiated,though in one embodiment, the reaction mixture is left to sit whileirradiating. In an alternative embodiment, the reaction mixture may beirradiated with UV light, or without visible light. In anotheralternative embodiment, the reaction mixture may be subjected todifferent temperatures and pressures than ones described herein, and/oran electric current in order to catalyze the oxidation of thecycloalkane to the cycloalkanol and/or cycloalkanone.

Photocatalytic oxidations often start from separation of photogeneratedelectron-hole pairs, which may lead to formation of intermediateradicals such as hydroxyl radicals (.OH) in the presence of molecularoxygen and/or peroxides. It was reported that Al₂O₃, TiO₂ and ZrO₂ dopedwith Pt exhibited oxidative activity of cyclohexane to cyclohexanone andcyclohexanol [Hammoumraoui I R, Braham A C, Roy L P and Kappenstein C2011, Catalytic oxidation of cyclohexane to cyclohexanone andcyclohexanol by tert-butyl hydroperoxide over Pt/oxide catalysts Bull.Mater. Sci. 34, 1127, incorporated herein by reference in its entirety].In terms of the present disclosure, radical species may interact withreactants e.g. cycloalkanes in the reaction mixture to form oxidizedalcohol and more oxidized ketone derivatives. Factors contributing tothe enhancement of the catalytic activity of the doped Pt/SrTiO₃photocatalyst compared to the bare SrTiO₃ nanoparticles include (i)prevention of the recombination of electron-hole pairs by Pt atoms inPt/SrTiO₃ photocatalysts, as the doped metal atoms often act as electrontraps [Mohamed R M, McKinney D L and Sigmund W M 2012. Enhancednanocatalysts Mater. Sci. Eng. R 73, 1, incorporated herein by referencein its entirety], (ii) a decrease of band gap energy which allowsabsorption of photons in the visible region and (iii) promotion ofinterfacial electron transfer process as Pt atoms lead to formation ofSchottky barriers on the SrTiO₃, which function as electron traps andfacilitate electron-hole separation. In a preferred embodiment,irradiation of the reaction mixture may induce the Pt/SrTiO₃photocatalyst to photocatalytically convert the cycloalkane to acycloalkanol and/or a cycloalkanone. Preferably the photocatalyticconversion oxidizes one or more alkyl functionalities of the cycloalkaneto hydroxyl or ketone groups, though in an alternative embodiment, otherreactions may occur. In a preferred embodiment, the oxidation processhas a molar conversion of the cycloalkane to the cycloalkanol and/or thecycloalkanone of greater than 40%, preferably greater than 60%,preferably greater than 70%, preferably greater than 80%, preferablygreater than 90%, preferably greater than 95%. In one embodiment, amixture of different cycloalkanes may be converted to a mixture ofdifferent cycloalkanols and different cycloalkanones. In an alternativeembodiment, the Pt/SrTiO₃ photocatalyst may catalyze a cycloalkane to acycloalkanol and/or a cycloalkanone without light irradiation but withhigh temperature, high pressure, and/or an electric current.

In one or more embodiments, the platinum is present in an amount of1.3-3.0 wt %, preferably 1.4-2.0 wt %, or about 1.5 wt % relative to atotal weight of the Pt/SrTiO₃ photocatalyst, the reaction mixture isirradiated with the light for 1 to 4 hours, preferably 1.2 to 3 hours,or about 1.5 hours, and the process has a molar conversion of thecycloalkane to the cycloalkanol and/or cycloalkanone of greater than95%, preferably greater than 96%, preferably greater than 97%,preferably greater than 98%, preferably greater than 99%, preferablygreater than 99.5%.

In one or more embodiments, the cycloalkane is cyclohexane, thecycloalkanol is cyclohexanol and the cycloalkanone is cyclohexanone. Inone embodiment, the formed cycloalkanol and/or the cycloalkanone remainin the reaction mixture but may be quantified by gas chromatography (GC)and/or liquid chromatography (LC). In an alternative embodiment, theformed cycloalkanol and/or the cycloalkanone may be separated from thereaction mixture and purified. In one embodiment, a mixture ofcycloalkanol and cycloalkanone is formed at a molar ratio of 100:1 to1:100, preferably 50:1 to 1:50, preferably 10:1 to 1:10, preferably 5:1to 1:5 during the oxidizing process. In an alternative embodiment, onlycycloalkanol is formed during the process. In another embodiment, onlycycloalkanone is formed during the process. The identity and ratio ofthe isolated cycloalkanol and cycloalkanone may be analyzed by nuclearmagnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy,high-performance liquid chromatography (HPLC), and/or gas chromatography(GC).

In one or more embodiments, the process further comprises recovering thePt/SrTiO₃ photocatalyst after the irradiating to obtain a recoveredPt/SrTiO₃ photocatalyst, and reusing the recovered Pt/SrTiO₃photocatalyst. The recovered Pt/SrTiO₃ photocatalyst may maintainphotocatalytic activity for at least 4, preferably at least 8,preferably at least 12 reaction cycles. The recovering may or may notrequire washing and/or drying between reaction cycles. As definedherein, “maintaining photocatalytic activity” means that when recyclingand reusing the recovered Pt/SrTiO₃ photocatalyst, the photocatalyticactivity of forming the cycloalkanol and/or the cycloalkanone e.g.measured as the aforementioned molar conversion of the cycloalkane tothe cycloalkanol and/or cycloalkanone) remains within at least 90%,preferably at least 95%, more preferably at least 96% of its originalvalue.

The examples below are intended to further illustrate protocols forpreparing and characterizing Pt/SrTiO₃ photocatalyst, and assessing themethod of oxidizing a cycloalkane to a cycloalkanol and/or acycloalkanone using the Pt/SrTiO₃ photocatalyst. They are not intendedto limit the scope of the claims.

Example 1

Photocatalyst Preparation

Strontium titanate (SrTiO₃) nanoparticles were prepared by an ultrasonicmethod. 0.3 mole of strontium acetate was added under a nitrogenatmosphere to 16 mol glacial acetic acid and stirred for 2 h at roomtemperature. Then, 5 mol titanium isopropoxide was added to the solutionmentioned above and the resulting mixture was stirred at roomtemperature for 6 h. Then, 20 mL of acetone was added and the resultingmixture was put in an apparatus for low-frequency ultrasound (Bransonic42 kHz) for 1 h. The resulting material was dried at 100° C. for 24 h,then calcined at 550° C. for 5 h in air. A photo-assisted deposition(PAD) route was used to prepare Pt/SrTiO₃ photocatalysts which containdifferent wt % of Pt metal (0.5, 1.0, 1.5 and 2.0 wt %). In this route,Pt metal was deposited on SrTiO₃ nanoparticles using an aqueous solutionof platinum chloride while applying UV light irradiation. The obtainedsamples were dried at 60° C. for 24 h and treated with H₂ (20 mL min⁻¹)at 60° C. for 2 h.

Example 2

Photocatalyst Characterization

The crystalline phase of the strontium titanate (SrTiO₃) nanoparticlesand Pt/SrTiO₃ photocatalysts was determined using powder X-raydiffraction (XRD) (Bruker axis D8 instrument) using CuKα radiation(λ=1,540 Å) in the 20 range from 10° to 80° at room temperature. Thechemical state information of the photocatalysts was determined usingX-ray photoelectron spectroscopy (XPS) (Thermo Scientific K-ALPHAspectrometer). The morphological structure of the strontium titanate(SrTiO₃) nanoparticles and Pt/SrTiO₃ photocatalysts was examined using atransmission electron microscope (TEM) (JEOL-JEM-1230). Specimens forTEM analysis were prepared by dispersing the nanoparticles in ethanoland placing one drop onto a holey-carbon-coated copper supported grid.The specific surface area was determined from nitrogenadsorption/desorption isotherms which were measured at 77 K using a Nova2000 series Chromatech. Prior to the analysis, the samples wereoutgassed at 150° C. for 24 h. UV-Vis-NIR spectrophotometer (V-570,Jasco, Japan) equipped with a standard cell for solid materials (Jasco,Japan) was used to estimate the band gap energy in air at roomtemperature by measuring ultra violet-visible diffuse reflectance(UV-Vis-DRS) spectra over the range of 200 to 800 nm. Shimadzu RF-5301fluorescence spectrophotometer was used to measure the photoluminescenceemission spectra (PL).

Example 3

Characterization of Strontium Titanate Nanoparticles and Pt SrTiO₃Photocatalysts

FIG. 1 illustrates XRD patterns of the strontium titanate (SrTiO₃)nanoparticles and Pt/SrTiO₃ photocatalysts. The obtained XRD patterns ofthe strontium titanate (SrTiO₃) nanoparticles and Pt/SrTiO₃photocatalysts reveal characteristic peaks of SrTiO₃, suggesting thatdoping strontium titanate nanoparticles with Pt does not significantlyaffect their structure. Furthermore, the characteristic XRD peaks ofplatinum or platinum oxide were not detected, which could be attributedto the fact that the weight percent platinum was lower than thedetection limit and/or good dispersion of Pt on the SrTiO₃ nanoparticlessurface was achieved. The same phenomenon was observed when oxomolybdatespecies dispersed over TiO₂ which was used for direct methanol oxidation[Faye J. Capron M. Takahashi A, Paul S. Katryniok B, Fujitani T andDumeignil F 2015. Effect of dispersion on to dimethoxymethane overMoOx/TiO₂ Energy Sci Eng. 3, 115, incorporated herein by reference inits entirety].

In addition, it was observed that the intensity of the characteristicSrTiO₃ peak decreased as the weight percentage of doped platinumincreased, especially at 32.15°. Scherer equation was used to calculatethe crystallite size based on the half-width of the most intense peak at2θ=32.15°. The calculated crystallite size were 24.0, 20.0, 17.0, 14.0and 12.0 nm for SrTiO₃, 0.5 wt % Pt/SrTiO₃, 1.0 wt % Pt/SrTiO₃, 1.5 wt %Pt/SrTiO₃ and 2.0 wt % Pt/SrTiO₃, respectively.

FIGS. 3A and 3B are TEM images of SrTiO₃ and 1.5 wt % Pt/SrTiO₃photocatalyst. These images demonstrate that SrTiO₃ is a sphericalnanoparticle as shown in FIG. 3A and platinum was doped as dots as shownin FIG. 3B. Table 1 summarizes BET specific surface area of SrTiO₃nanoparticles and Pt/SrTiO₃ photocatalysts calculated according to theBET adsorption isotherm model. The calculated BET surface area were 20,18, 16, 14 and 10 m²/g for SrTiO₃, 0.5 wt % Pt/SrTiO₃, 1.0 wt %Pt/SrTiO₃, 1.5 wt % Pt/SrTiO₃, and 2.0 wt % Pt/SrTiO₃, respectively.

TABLE 1 BET surface area of SrTiO3 and Pt-doped SrTiO3 nanoparticlesSample S_(BET) (m²/g) SrTiO₃ 20 0.5 wt % Pt doped SrTiO₃ 18 1.0 wt % Ptdoped SrTiO₃ 16 1.5 wt % Pt doped SrTiO₃ 14 2.0 wt % Pt doped SrTiO₃ 10

FIG. 4 demonstrates UV-Vis-DRS spectra of SrTiO₃ nanoparticles andPt/SrTiO₃ photocatalysts. The results reveal that SrTiO₃ nanoparticlesabsorb the UV region (368 nm). However, the absorption peaks ofPt/SrTiO₃ photocatalysts were shifted to longer wavelength (˜375 nm,˜373 nm, ˜370 nm, and ˜366 nm for 0.5 wt % Pt/SrTiO₃, 1.0 wt %Pt/SrTiO₃, 1.5 wt % Pt/SrTiO₃, and 2.0 wt % Pt/SrTiO₃, respectively).Similar trend was observed earlier when titania nanotubes were dopedwith Pt [Vijayan B K, Dimitrijevic N M, Wu J and Gray K A 2010. Theeffects of Pt doping on the structure and visible light photoactivity oftitania nanotubes J. Phys. Chem. C 114, 21262, incorporated herein byreference in its entirety]. The band gap (Eg) for SrTiO₃ and Pt/SrTiO₃photocatalysts was calculated from the UV-Vis-DRS spectra by usingTauc's relation [Chrysicopoulou P, Davazoglou D, Trapalis C and Kordas G1998 Photocatalytic destruction of methylene blue on Ag@TiO₂ withcore/shell structure Thin Solid Films 323, 188, incorporated herein byreference in its entirety]:αhν=B(hν−E _(g))^(n)where α is the optical absorption coefficient, E (=hc/λ) is the photonenergy, B is a constant, λ is the measured wavelength in nm, E_(g) isthe optical band gap, and n is ½ or 2 for direct or indirect band gapsemiconductor, respectively. FIG. 5 shows the linear part of the plot of((αhν)² vs. αh, while E_(g) values were estimated by extrapolating eachplot to its baseline which were presented in Table 2. It is clear thatband gap energy for Pt-doped photocatalysts are smaller than those forSrTiO₃ nanoparticles, and the band gap energy values can be tuned byweight percentage of the doped Pt.

TABLE 2 Band gap energies of SrTiO₃ arid Pt-doped SrTiO₃ nanoparticles(Pt/SrTiO₃ photocatalysts) Sample Band gap energy eV SrTiO₃ 3.60 0.5 wt% Pt doped SrTiO₃ 3.10 1.0 wt % Pt doped SrTiO₃ 2.98 1.5 wt % Pt dopedSrTiO₃ 2.85 2.0 wt % Pt doped SrTiO₃ 2.75

FIG. 6 illustrates the PL spectra of the SrTiO₃ and Pt/SrTiO₃photocatalysts. The results show that peak intensity of the PL forSrTiO₃ reduced as the Pt weight percentage increased from 0 to 1.5%,however, no further enhancement of peak intensity was observed beyondthe Pt weight percentage at 1.5%, indicating the significant effect ofdoping SrTiO₃ with Pt by influencing the rate of the electron-holerecombination. This observation may be due to the formation of Schottkybarriers on the SrTiO₃ upon Pt deposition, which might serve as electrontraps. These electron traps would facilitate the electron-holeseparation and promote the interfacial electron transfer process, thusmake the photocatalyst more efficient [Grabowska E, Marchelek M,Klimczuk T, Lisowski W and Zaieska-Medynska A 2017, TiO₂/SrTiO₃ andSrTiO₃ microspheres decorated with Rh, Ru or Pt nanoparticles: HighlyUV-vis responsible photoactivity and mechanism J. Catal. 350, 159,incorporated herein by reference in its entirety].

Example 4

Photocatalytic Oxidation of Cyclohexane: Experimental

Photocatalytic experiments were performed by feeding a N₂ stream at 30L/h (STP) containing 200 ppm cyclohexane, 10 vol. % O₂ at a temperatureof 60° C. and a reaction pressure of 1 atm. Nitrogen functioned as thecarrier gas for cyclohexane. Additionally, 320 ppm of water vaporizedfrom 60° C. controlled saturators was added in order to minimizephotodeactivation of the catalyst. A fluidized bed photoreactor was usedas the reactor, which was irradiated by a Xenon lamp covered by acut-off filter of 420 nm with a power of 300 W and an intensity of 0.96W/cm². The catalytic bed was composed of 1.2 g of photocatalyst mixedwith 20 g glass spheres in order to improve the fluidization property.The reactor inlet reactants and outlet products were analyzed using gaschromatography (Agilent GC 7890A model). The reactor was irradiatedafter complete adsorption of cyclohexane on the catalyst surface. Thephotocatalytic behavior of all analyzed samples was evaluated as:X=(C ₀ C ₁)/C ₀×100%where X=cyclohexane conversion, C₀=inlet cyclohexane concentration, andC₁=outlet cyclohexane concentration.

Example 5

Photocatalytic Oxidation of Cyclohexane: Results and Discussion

FIG. 7 shows the effect of the doped Pt weight percentage on thephotocatalytic activities of SrTiO₃ nanoparticles and Pt/SrTiO₃photocatalysts for photocatalytic oxidation of cyclohexane. The resultsshow that the photocatalytic activity was significantly enhanced, asdemonstrated by increasing conversion of cyclohexane of 5.0%, 75%, 85%,and 100% by using SrTiO₃, 0.5 wt % Pt/SrTiO₃, 1.0 wt % Pt/SrTiO₃, 1.5 wt% Pt/SrTiO₃, and 2.0 wt % Pt/SrTiO₃, respectively. Such enhancement incatalytic activity due to the doping SrTiO₃ nanoparticles with noblemetals such as Pt [Neppolian B, Mine S, Horiuchi Y, Bianchi C L,Mat-suoka M, Dionysiou D D and Anpo M 2016. Efficient photocatalyticdegradation of organics present in gas and liquid phases usingPt—TiO₃/Zeolite (H-ZSM) Chemosphere 153, 237, incorporated herein byreference in its entirety]. Moreover, the photocatalytic activity didnot change after weight percentage of doped metallic Pt reached 1.5 wt%. Therefore, the weight percentage of doped metallic Pt affected theelectron-hole recombination rate and band gap of SrTiO₃ nanoparticles.Nevertheless, it can be concluded that 1.5 wt % Pt/SrTiO₃ photocatalystexhibited the uppermost photocatalytic activity, lowest electron-holerecombination rate and band gap.

The stability of the Pt/SrTiO₃ nanoparticles for the photocatalyticoxidation of cyclohexane was investigated using the 1.5 wt % Pt/SrTiO₃photocatalyst. It was verified that the 1.5 wt % Pt/SrTiO₃ photocatalystmaintained high photocatalytic stability after being used fivesuccessive times [Pol R, Guerrero M, Garcia-Lecina E, Altube A,Rossinyol E, Garroni S, Baró M D, Pons J. Sort J and Pellicer E 2016,Ni-, Pt- and (Ni/Pt-doped TiO₂ nanophotocatalysts: A smart approach forsustainable degradation of Rhodamine B dye Appl Catal, B 181, 270,incorporated herein by reference in its entirety].

The invention claimed is:
 1. A process of oxidizing a cycloalkane to acycloalkanol and/or a cycloalkanone, the process comprising: contactinga feed mixture comprising the cycloalkane and an oxidant with aPt/SrTiO₃ photocatalyst thereby forming a reaction mixture; andconcurrently irradiating the reaction mixture with light thereby formingthe cycloalkanol and/or the cycloalkanone; wherein the Pt/SrTiO₃photocatalyst comprises: strontium titanate nanoparticles; and platinumdoped on a surface of the strontium inmate nanoparticles; wherein theplatinum is present in an amount of 0.1-5.0 wt % relative to a totalweight of the Pt/SrTiO₃ photocatalyst.
 2. The process of claim 1,wherein the Pt/SrTiO₃ photocatalyst has a crystallite size of 8-30 nm.3. The process of claim 1, wherein the Pt/SrTiO₃ photocatalyst has a BETsurface area of 5-25 m²/g.
 4. The process of claim 1, wherein thePt/SrTiO₃ photocatalyst has an absorption peak in a range of 360-380 nm,and a band gap energy of 2.5-3.6 eV.
 5. The process of claim 1, whereinthe Pt/SrTiO₃ photocatalyst has a photoluminescence peak in a range of380-480 nm upon excitation at a wavelength of 270-290 nm.
 6. The processof claim 1, wherein the light has a wavelength of 400-800 nm.
 7. Theprocess of claim 1, wherein the feed mixture is contacted with thePt/SrTiO₃ photocatalyst at a pressure of 0.5-2 atm.
 8. The process ofclaim 1, wherein the feed mixture is contacted with the Pt/SrTiO₃photocatalyst at a temperature of 40-80° C.
 9. The process of claim 1,wherein the cycloalkane is present in the feed mixture at aconcentration of 10-400 ppm.
 10. The process of claim 1, wherein theoxidant is present in an amount of 5-30 vol. % relative to a totalvolume of the feed mixture.
 11. The process of claim 1, wherein thePt/SrTiO₃ photocatalyst is present at a concentration of 0.2-5.0 g ofphotocatalyst per liter of the reaction mixture.
 12. The process ofclaim 1, wherein the oxidant is O₂.
 13. The process of claim 1, whereinthe feed mixture further comprises an inert gas.
 14. The process ofclaim 1, wherein the feed mixture further comprises water.
 15. Theprocess of claim 1, which has a molar conversion of the cycloalkane tothe cycloalkanol and/or the cycloalkanone of greater than 40%.
 16. Theprocess of claim 1, wherein the cycloalkane is cyclohexane, thecycloalkanol is cyclohexanol, and the cycloalkanone is cyclohexanone.17. The process of claim 1, wherein the platinum is present in an amountof 1.3-3.0 wt % relative to a total weight of the Pt/SrTiO₃photocatalyst; wherein the reaction mixture is irradiated with light for1 to 4 hours; and wherein the process has a molar conversion of thecycloalkane to the cycloalkanol and/or cycloalkanone of greater than95%.
 18. The process of claim 1, further comprising: recovering thePt/SrTiO₃ photocatalyst after the irradiating to obtain a recoveredPt/SrTiO₃ photocatalyst; and reusing the recovered Pt/SrTiO₃photocatalyst, which maintains photocatalytic activity for at least 4reaction cycles.